The concept of simplified entropy is proposed and applied in detecting the location of power quality disturbances combined with Mathematical Morphology; Firstly,a morphological filter with adaptive structure elements is designed in the theory of mathematical morphology to filter noises and harmonics. Then, the concept of simplified entropy is proposed based on the theory of information entropy, and used to show the stability of the signal for each time to obtain a singular point. Finally, the validity of the method is analyzed and compared in different conditions of the amplitude,harmonic content and white noise variance,the simulation results show that this method can quickly and effectively detect the disturbances duration in the case of multiple interference.